The login information is invalid on one computer to login to the administration section of WordPress, but on another computer the same exact login information works just fine.
I have already disabled all the plugins to see if that was a problem.
I already had my client clear her cache and cookies.
She did a system reboot of her computer.
I created a new username and password, which continued to not work on her computer and worked fine on mine.
I have seen similar questions on the forums, but none of them had the exact same issue.